Do brain tissue transplants alter personal identity? Inadequacies of some "standard" arguments

Currently, brain tissue transplantations are being developed as a clinical-therapeutic tool in neurodegenerative diseases such as Parkinson's or Alzheimer's disease. From an ethical point of view, distinguishing between the preservation and an alteration of personal identity seems to be central to determining the scope for further application of brain tissue transplantation therapy. The purpose of this article is to review "standard" arguments which are used on the one hand by proponents to prove preservation of personal identity and by opponents on the other hand to prove that brain tissue transplantation results in an altered personal identity. Proponents and opponents are shown to use the same arguments, albeit with different presuppositions. These presuppositions concern the meaning of the term "identity", either numerical or qualitative, the definition of brain identity, either structurally or functionally, and the relationship between mental states, psychological functions and neurophysiological properties as criteria for personal identity. Furthermore the respective neurophysiological, clinical and philosophical evidence for the different presuppositions are discussed. It is concluded that evaluation of personal identity in brain tissue transplantation should not only rely on the "standard" arguments but, additionally, neurophysiological, clinical and philosophical implications should be discussed.